PDE3, PDE4 and PKC regulate local Ca2+ releases and cardiac pacemaker firing

为了验证（PDE3+PDE4）联合活性通过调节cAMP/PKA信号影响基础自发SANC放电的假设，我们使用了磷酸蛋白（PLB）在Ser16位点的磷酸化作为SANC中cAMP/PKA依赖性蛋白磷酸化的标记。特异性PDE3抑制剂西洛胺（cilostamide, 0.3 mkmol/L）或PDE4抑制剂罗利普兰（rolipram, 2 mkmol/L）可使PLB磷酸化增加20%，但Cil+Rol联合使用可使PLB磷酸化增加110%，其效果与广谱PDE抑制剂IBMX相似（140%）。L型Ca2+电流（ICa，L）保证了LCR的存在，为sr提供了可泵送的Ca2+。Cil或Rol单独使ICa，L的幅度分别增加了60%和4%，而（Cil+Rol）或IBMX使ICa，L增加了100%。西洛他胺使SANC自发放电速率（穿孔膜片钳）增加20%（从14813到17513次/分钟，n=8），而罗利普兰在2、20和100 mkmol/L时没有加速自发放电。与IBMX相似，（Cil+Rol）使SANC自发心跳率提高了50%（从1348次心跳/分钟增加到19711次心跳/分钟，n=9），其效果是由于LCR数量和大小的显著增加以及LCR周期的减少，这预示着自发周期长度的减少。当RyR被ryanodine禁用和lcr被废除时，IBMX和（Cil+Rol）都不能加速DD速率或增加SANC放电速率，这表明Ca2+循环在pde依赖性的自发搏动控制中起关键作用。我们得出结论，PDE3和PDE4都能调节自发的SANC放电，只有当PDE3和PDE4同时被抑制时，PDE4的关键作用才会被揭示。因此，（PDE3+PDE4）的协同作用抑制了基础cAMP/ pka依赖的PLB磷酸化，降低了ICa，L振幅，减少了RyR Ca2+的释放，延长了LCR周期，限制了自发的SANC放电速率。

To test the hypothesis that combined activity of (PDE3+PDE4) impacts on basal spontaneous SANC firing via regulation of cAMP/PKA signaling, we used phosphorylation of phospholamban (PLB) at Ser16 site as a marker of cAMP/PKA-dependent protein phosphorylation in SANC. Specific PDE3 inhibitor, cilostamide (Cil, 0.3 mkmol/L), or a PDE4 inhibitor, rolipram (Rol, 2 mkmol/L), increased PLB phosphorylation by 20%, but the combination of Cil+Rol increased PLB phosphorylation by 110%, an effect similar to that (140%) produced by broad spectrum PDE inhibitor IBMX. L-type Ca2+ current (ICa,L) ensures LCR existence, providing Ca2+ available for pumping in SR. Cil or Rol alone increased the amplitude of ICa,L by 60% and 4%, respectively, while (Cil+Rol) or IBMX increased ICa,L by 100%. Cilostamide increased the spontaneous SANC firing rate (perforated patch-clamp) by 20% (from 14813 to 17513 beat/min, n=8), while rolipram produced no acceleration of spontaneous firing at 2, 20 or 100 mkmol/L. Similar to IBMX, (Cil+Rol) increased the spontaneous SANC beating rate by 50% (from 1348 to 19711 beat/min, n=9), the effect was due to a marked increase in the LCR number, size and decrease in the LCR period that predicted the concomitant decrease in the spontaneous cycle length. When RyR were disabled by ryanodine and LCRs were abolished, both IBMX and (Cil+Rol) failed to accelerate DD rate or increase SANC firing rate indicating key role of Ca2+ cycling for PDE-dependent control of spontaneous beating. We conclude that both PDE3 and PDE4 regulate spontaneous SANC firing, and a crucial role of PDE4 is revealed only when PDE3 and PDE4 are concurrently inhibited. Thus, synergism of (PDE3+PDE4) suppresses basal cAMP/PKA-dependent PLB phosphorylation and reduces ICa,L amplitude to decrease RyR Ca2+ release, prolong the LCR period and limit the spontaneous SANC firing rate.